1. Field of the Invention
The present invention relates to an ultrasonic touch-position sensing device for sensing a touch position on a nonpiezoelectric plate by means of using first- and second transducer-units, a signal analyzer, and an amplifier.
2. Description of the Prior Art
Conventional touch panels include, in general, a wedge-shaped transducer for vibrating a nonpiezoelectric plate indirectly, or a piezoelectric thin film transducer for vibrating a nonpiezoelectric plate directly. Such conventional touch panels detect an output electric signal, which disappears in response to a disappearance of an ultrasound on a nonpiezoelectric plate by touching thereon, and sense a touch position from a disappearance of the output electric signal. Thus, conventional touch panels cause a high voltage operation with a high power consumption, and a large-scale circuit with a complicated structure. In addition, conventional touch panels do not have a structure for exciting an ultrasound directly on a transparent nonpiezoelectric plate in contact with a liquid crystal.
An object of the present invention is to provide an ultrasonic touch-position sensing device capable of detecting first- and second delayed electric signals by touching a nonpiezoelectric plate with a high sensitivity and a quick response time.
Another object of the present invention is to provide an ultrasonic touch-position sensing device excellent in manufacturing.
Another object of the present invention is to provide an ultrasonic touch-position sensing device operating under low electric power consumption with low voltage.
A still other object of the present invention is to provide an ultrasonic touch-position sensing device having a small-sized circuit with a simple structure which is very light in weight.
According to one aspect of the present invention there is provided an ultrasonic touch-position sensing device comprising a nonpiezoelectric plate, first- and second transducer-units, and a signal analyzer. The first transducer-unit consists of at least three input interdigital electrodes Txi (i=1, 2, . . . , m), at least three electrode groups Gxi (i=2, . . . , m) corresponding with the input interdigital electrodes Txi, respectively, firstand second piezoelectric substrates, and at least two uniting terminals Uxj (j=1, 2, . . . , n). The input interdigital electrodes Txi and the electrode groups Gxi are formed on first- and second edges, respectively, of an upper end surface of the nonpiezoelectric plate. The first- and second piezoelectric substrates are cemented on the input interdigital electrodes Txi and the electrode groups Gxi, respectively. Two neighbors of the electrode groups Gxi consist of at least two output interdigital electrodes Rxaj (j=1, 2, . . . , n) and at least two output interdigital electrodes Rxbj (j=1, 2, . . . , n), respectively. The output interdigital electrodes Rxaj have the reverse electrode-finger directions from the output interdigital electrodes Rxbj. The uniting terminals Uxj are connected to the output interdigital electrodes Rxaj, respectively, and also to the output interdigital electrodes Rxbj, respectively. The second transducer-unit has the same construction as the first transducer-unit, and consists of at least three input interdigital electrodes Tyi (i=1, 2, . . . , m), at least three electrode groups Gyi (i=1, 2, . . . , m), third- and fourth piezoelectric substrates, and at least two uniting terminals Uyj (j=1, 2, . . . , n). The input interdigital electrodes Tyi and the electrode groups Gyi are formed on third- and fourth edges, respectively, of the upper end surface of the nonpiezoelectric plate. The third and fourth piezoelectric substrates are cemented on the input interdigital electrodes Tyi and the electrode groups Gyi, respectively. Two neighbors of the electrode groups Gyi consist of at least two output interdigital electrodes Ryaj (j=1, 2, . . . , n) and at least two output interdigital electrodes Rybj (j=1, 2, . . . , n), respectively. The output interdigital electrodes Ryaj have the reverse electrode-finger directions from the output interdigital electrodes Rybj. The uniting terminals Uyj are connected to the output interdigital electrodes Ryaj, respectively, and also to the output interdigital electrodes Rybj, respectively.
When a first input electric signal is applied to two neighbors of the input interdigital electrodes Txi simultaneously, a first surface acoustic wave (SAW) is excited in the first piezoelectric substrate, The first SAW is transmitted to the second piezoelectric substrate along the upper end surface of the nonpiezoelectric plate, and transduced to a first output electric signal at the output interdigital electrodes Rxaj and Rxbj, respectively. Thus, ixc3x97j first-SAW lanes in all are formed between the input interdigital electrodes Txi and the electrode groups Gxi. In the same way, ixc3x97j second-SAW lanes in all are formed between the input interdigital electrodes Tyi and the electrode groups Gyi.
If touching nowhere on the upper end surface of the nonpiezoelectric plate, no delayed electric signal appears at all the uniting terminals. However, if touching anywhere on the upper end surface of the nonpiezoelectric plate, a first delayed electric signal appears twice without stopping at one of the uniting terminals Uxj, and a second delayed electric signal appears twice without stopping at one of the uniting terminals Uyj. Thus, it is possible to sense a touch position by clarifying which of the input interdigital electrodes Txi receives the first input electric signal twice without stopping and which of the input interdigital electrodes Tyi receives the second input electric signal twice without stopping when the first- and second delayed electric signals appear at one of the uniting terminals Uxj and one of the uniting terminals Uyj, respectively.
According to another aspect of the present invention there is provided a piezoelectric substrate with a window-flame shape in place of the first-, second-, third-, and fourth piezoelectric substrates.
According to another aspect of the present invention there are provided first-, second-, third-, and fourth piezoelectric substrates, made of a piezoelectric ceramic, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a transparent nonpiezoelectric plate.
According to another aspect of the present invention there are provided first-, second-, third-, and fourth piezoelectric substrates having a thickness smaller than an interdigital periodicity of the input interdigital electrodes Txi and Tyi. In addition, there is provided a nonpiezoelectric plate having a thickness larger than three times the interdigital periodicity.
According to another aspect of the present invention there is provided an ultrasonic touch-position sensing device, wherein the phase velocity of the surface acoustic wave on the nonpiezoelectric plate alone is higher than that in the first-, second-, third-, and fourth piezoelectric substrates alone.
According to another aspect of the present invention there are provided another nonpiezoelectric plate and a liquid crystal, which is sandwiched between two nonpiezoelectric plates.
According to other aspect of the present invention there is provided an amplifier connected between the signal analyzer and the input interdigital electrodes Txi and Tyi.
According to a further aspect of the present invention there are provided a first switch connected with the input interdigital electrodes Txi, and a second switch connected with the input interdigital electrodes Tyi.